The world's largest rainforest is ravaged by deforestation and two recent droughts. If they continue, says one expert, the Amazon risks entering a period where it can no longer be relied upon to absorb more greenhouse gas emissions than it produces.

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The Amazon rainforest is facing the combined threat of increasingly severe droughts and continuing deforestation that could wipe out large areas of the forest, warned a respected forest scientist this week.

In a groundbreaking study published in the journal Science earlier this year, Dr Simon Lewis, of Leeds University, found the 2010 drought in the Amazon was more widespread than the 2005 one, previously thought of as a once-in-a-century event.

In an interview with the Ecologist he now says if greenhouse gases are the cause of the severe droughts and such droughts are repeated three or more times a decade it could set in motion a vicious cycle by which droughts would lead to higher emissions of carbon dioxide from rotting trees and, in turn, potentially more frequent and severe droughts.

"If the climate changes in the Amazon to a regime with more severe and frequent droughts, then the dead trees may be numerous enough to cancel-out all the usual carbon uptake, and perhaps even add carbon dioxide to the atmosphere...our current emission pathways are, to be blunt, playing Russian roulette with a substantial portion of the world's largest rainforest," he says.